The present invention relates to internal combustion engines; and more particularly to the ignition system for such engines.
In an internal combustion engine, the fuel in a cylinder is ignited by a spark plug at a prescribed point during the combustion cycle of the engine. For example, it is often desirable to ignite the fuel in advance of the moment at which the piston reaches the top dead center point in the cylinder.
Various types of ignition systems have been developed for four cycle gasoline engines. One type of ignition system employs a set of breaker points which act as a switch. A cam, that is mechanically coupled to the crank shaft of the engine, opens and closes the points at a given rotational angle, thereby controlling the flow of electricity to an ignition coil. When the points are opened, the magnetic field within the ignition coil collapses inducing a high voltage across a secondary winding of the coil. The secondary winding is connected to the spark plug and the high voltage causes a spark which ignites the fuel in the cylinder. The points, as well as the spark plug, wear over time and must be replaced occasionally.
The moment in the cycle at which the spark occurs must be regulated to insure maximum performance of the engine at different speeds. The initial burning of the fuel occurs during a relatively constant interval, which corresponds to an increased number of crankshaft degrees as the speed of the engine increases. As a consequence, a centrifugal mechanism often is used to advance the angle at which the cam opens the points as the engine speed increases. Typically, a weight is attached to either the cam or the breaker points so that as the engine speed increases the movement of the weight under centrifugal force effectively advances the angular position of the cam relative to the crankshaft. In this new position, the points open at an earlier time than before, which advances the spark within the engine cycle.
U.S. Pat. No. 3,484,677 discloses a breakerless ignition system having an energizing coil in which electrical energy is induced by a rotating permanent magnet to provide power for creating an ignition spark. The fixed timing of the ignition is controlled by an electronic circuit which includes an electronic switch and a control coil. Electric current induced in the control coil by the rotating permanent magnet closes the switch causing the induced current to flow through the energizing coil and producing a spark that ignites the fuel in the cylinder.
Although this latter type of ignition system overcomes some of the problems associated with breaker points, it does not provide a mechanism by which the spark can be advanced or retarded with engine speed.